From b8ae09f01c2bf4696d17d7c46a1fb5d5f0c245a5 Mon Sep 17 00:00:00 2001
From: "rread@ubuntu.eng.hq.xensource.com" <rread@ubuntu.eng.hq.xensource.com>
Date: Mon, 28 Nov 2005 15:34:00 -0700
Subject: [PATCH] The device sharing check races when more than one file backed
 vbd is configured. Both of the files pick the same free loop device in the
 for loop, and then one fails to losetup.  This patch will now retry if
 losetup fails until it succeeds or no more devices are available.

Signed-off-by: Robert Read <robert@xensource.com>
---
 tools/examples/block | 88 ++++++++++++++++++++++----------------------
 1 file changed, 45 insertions(+), 43 deletions(-)

diff --git a/tools/examples/block b/tools/examples/block
index 0a98344ca5..04a00432ff 100644
--- a/tools/examples/block
+++ b/tools/examples/block
@@ -202,59 +202,61 @@ case "$command" in
 mount it read-write in a guest domain."
         fi
 
-        loopdev=''
 
-	for dev in /dev/loop*
-        do
-          if [ ! -b "$dev" ]
-          then
-            continue
-          fi
-
-          f=$(losetup "$dev" 2>/dev/null) || f='()'
-          f=$(echo "$f" | sed -e 's/.*(\(.*\)).*/\1/g')
-
-          log err "$file $f $dev"
-
-          if [ "$f" ]
-          then
-            # $dev is in use.  Check sharing.
-
-            if [ "$mode" == 'no' ]
+	while true
+        do 
+          loopdev=''
+          for dev in /dev/loop*
+          do
+            if [ ! -b "$dev" ]
             then
               continue
             fi
 
-            f=$(readlink -f "$f")
+            f=$(losetup "$dev" 2>/dev/null) || f='()'
+            f=$(echo "$f" | sed -e 's/.*(\(.*\)).*/\1/g')
+
+            log err "$file $f $dev"
 
-            if [ "$f" == "$file" ]
+            if [ "$f" ]
             then
-              check_file_sharing "$file" "$dev" "$mode"
+              # $dev is in use.  Check sharing.
+              if [ "$mode" == 'no' ]
+              then
+                continue
+              fi
+
+              f=$(readlink -f "$f")
+
+              if [ "$f" == "$file" ]
+              then
+                check_file_sharing "$file" "$dev" "$mode"
+              fi
+            else
+              # $dev is not in use, so we'll remember it for use later; we want
+              # to finish the sharing check first.
+              
+              if [ "$loopdev" == '' ]
+              then
+                loopdev="$dev"
+              fi
             fi
+          done
+
+          if [ "$loopdev" == '' ]
+          then
+            fatal 'Failed to find an unused loop device'
+          fi
+          if losetup "$loopdev" "$file"
+          then
+	    log err "mapped $file using $loopdev"
+            xenstore_write "$XENBUS_PATH/node" "$loopdev"
+            write_dev "$loopdev"
+            exit 0
           else
-            # $dev is not in use, so we'll remember it for use later; we want
-            # to finish the sharing check first.
-            
-            if [ "$loopdev" == '' ]
-            then
-              loopdev="$dev"
-            fi
+            log err "losetup $loopdev $file failed, retry"
           fi
-        done
-
-        if [ "$loopdev" == '' ]
-        then
-          fatal 'Failed to find an unused loop device'
-        fi
-
-        if losetup "$loopdev" "$file"
-        then
-          xenstore_write "$XENBUS_PATH/node" "$loopdev"
-          write_dev "$loopdev"
-          exit 0
-        else
-          fatal "losetup $loopdev $file failed"
-        fi
+	done
 	;;
     esac
     ;;
-- 
2.30.2